Radiology
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How can X-rays on a graph be systematically shown?
As a sine wave
What is the speed of light?
3x10(8)ms-1
What is the name of the innermost electron shell?
The K shell
What is the name of the energy that must be exceeded in order to remove an electron from its shell
The binding energy must be exceeded
Which electron shell has the highest binding energy
The closer the electron is to the nucleas the higher the binding energy - K has the highest binding energy
How can you work out the specific amount of energy required to move an electron to an outer shell
The energy required to move an electron to an outer shell is the difference in the binding energey of the shells
What kind of current does X-ray production require?
X-ray production requires a unidirectional current
X-ray production requires a uni-directional current but xray units are powered by alternating current. The units have a generator to modify this so that it mimics a direct current. What is this change called?
Refraction
Does divergence decrease or increase with distance from the xray source?
Divergence decreases with the distance from the xray source
What is the inverse square law
Intensity beam is inversely proportional to the square of the distance between the xray source and the point of measurement Therefore if you DOUBLE the distance you will quarter the dose
What is the purpose of the glass envelope in the xray tube
The glass component acts as a vacuum to ensure the electrons are not hindered by gas molecules
Why does the metal sheielding tend to be made of lead
This absorbs the X-rays
What sis the purpose of the aluminium filtration?
This removes the lower energy, non diagnostic X-rays from the Bea,
What is the purpose of the oil in the xray tube head
This dissipates the heat produced by the xray tube by thermal convection
The spacer cone provides the ‘focus to skin distance’’ what is this distance?
200mm
What is the purpose of the collimator
This is a lead diaphragm attached to the end of the spacer cone and this acts too reduce the patient dose
What is the benefit of rectangular collimation
It can potentially reduce surface area irradiated by almost 50% It can also improve image contrast by reducing scatter
What is the penumbra affect and why one’s it happen?
This is blurring of the radiogrpahic image due to the focal spot not being a single point but rather a small area
How can the penumbra affect be reduced
This can be minimised by shrinking the focal spot
What are the three fates of X-ray photons emitted from the focal spot.
• Attenuated by the lead sheilding • Attenuated by the aluminium filtration • Exit tube-head to form the x-ray beam
Describe continuous radiation
Bombarding electrons interacts with the nucleas of the target atom, causing the electrons to be rapidly decelerated and deflected - kinetic energy released as xray photons. Produces a continuous range of xray photon energies
Describe characteristic radiation
Bombarding electrons interact with inner electron shells target atom, photon energies depend on the binding energies of the electron shells Produces specific energies of xray photon, characteristic to the element used for that target
What does it mean if an electron has been ionised
It has been displaced entirely
What does it mean if an electron has become excited
It has moved to an upper shell